Fill bezier curve with Convert To
The First way to do this...

( This will work independent of the axis you created your curve object.)


Select your curve.
Hit spacebar and search for "convert to" Shortcut (ALT + C)
Select "Mesh from curve"
If you have not turned on "Mesh : F2" addon do so in the user preference.
Enter edit mode with the converted curve selected.
Select all the edges and hit F to fill.


-

The second way to go.

(For this method your curve needs to be created in the top view OR in another 
words the XY axis)


Select your curve.
Go to Properity panel > Bezier Tab > Shape > turn on 2D shape Button.
Make sure "cyclic" is turn on.
Select "front" on the fill option.


Cheers let me know if it helps.